As shown in FIG. 6, in a mobile communication system supporting the LTE (Long Term Evolution)-Advanced, a mobile station UE can perform CA (Carrier Aggregation) communication by using a macrocell #1 as a Pcell which is a serving cell in a PCC (Primary Component Carrier, a main carrier), and using a picocell #1 as an Scell which is a serving cell in an SCC (Secondary Component Carrier, a sub-carrier), under control of a radio base station eNB#1.
Here, when handover procedures are performed for switching the Pcell of the mobile station UE from the macrocell #1 under control of the radio base station eNB#1 to a macrocell #2 under control of a radio base station eNB#2, the mobile station UE deletes the picocell #1 previously set as the Scell under control of the radio base station eNB#1.
Specifically, as shown in step 7 in FIG. 7, the mobile station UE deletes the picocell #1 previously set as the Scell under control of the radio base station eNB#1 in accordance with “mobilityControlInformation” included in “RRC Connection Reconfiguration.”
Meanwhile, when the mobile station UE is instructed to set the picocell #1 as the Scell under control of the radio base station eNB#2 by the “mobilityControlInformation” included in the “RRC Connection Reconfiguration,” the mobile station UE sets the picocell #1 in a deactivated state under control of the radio base station eNB#2.
In the meantime, as shown in FIG. 8, in the mobile communication system supporting the LTE-Advanced, when the picocell #1 is deployed near a boundary between the macrocell #1 and the macrocell #2 under control of the radio base station eNB#1, the picocell #1 can be continuously used as the Scell after the handover procedures are performed for switching the Pcell of the mobile station UE from the macrocell #1 to the macrocell #2.